precautions for bootcamp; 56yo female

I am starting a new, more vigorous fitness program to combat post-hysterectomy body fat. It is a bootcamp available for all ages, and I expect I will be above the typical age as a new participant. I dont necessarily have a lot of extra weight (I am 5.5 and weigh 134 lbs) however, I am unfit and my waist measurement and BMI are well out of bounds. I do not do much weight training, and my trainer will incorporate that to my regimen. I expect to have soreness and fatigue. How do I know what I am capable of without getting hurt? I dont have an athletic history, most of my current exercise program is cardio based. Thanks for your input.